Respiratory muscles performance is related to oxygen kinetics during maximal exercise and early recovery in patients with congestive heart failure

Abstract

Background - Dyspnea and fatigue are the main causes of exercise limitation in chronic heart failure (CHF) patients, whose peak inspiratory (Pi(max)) and expiratory pressures (Pe(max)) are often reduced. The aim of this study was to examine the relationship between respiratory muscle performance and oxygen kinetics. Methods and Results - A total of 55 patients (NYHA class I to III) and 11 healthy subjects underwent cardiopulmonary exercise tests (CPET) on a treadmill. In 45 of the 55 patients (group I) and in healthy subjects (group II), pulmonary function tests, Pi(max), and Pe(max) were measured before and 10 minutes after exercise, and oxygen kinetics were monitored throughout and during early recovery from CPET. The first degree slope of oxygen consumption (V̇O2) decline during early recovery (V̇O2/t-slope) and V̇O2 half-time (T( 1/2 )) were calculated. In 10 of the 55 CHF patients (group III), the measurements of Pi (max) were repeated 2, 5, and 10 minutes after CPET. A > 10% reduction in Pi(max) after CPET (subgroup IA) was measured in 11 of 45 patients. In contrast, 34 of 45 CHF patients (subgroup IB) and all control subjects (group II) had Pi(max)>90% of baseline value after CPET. Subgroup IA patients had significantly lower peak V̇O2 (13.5±2.1 versus 17.8±5.6 mL · kg-1 · min-1; P<0.001), lower anaerobic thresholds (10.1 ±2.4 versus 13.6±4.6 mL · kg-1 · min-1; P=0.003) and lower Vo2/t-slopes (0.365±0.126 versus 0.519±0.227 L · min-1 · min-1; P=0.008) than subgroup IB patients. Conclusions - The reduction of Pi(max) after exercise is associated with prolonged early recovery of oxygen kinetics, which may explain, in part, the role played by respiratory muscles in exercise intolerance in CHF patients.